Attached matter detector, and attached matter detection method

Abstract

An attached matter detector includes: a light source that emits light to a transparent member; imaging device that receives light emitted from the light source and reflected by an attached matter on the transparent member, and consecutively images an image of the attached matter at a predetermined imaging frequency; and an attached matter detection processor that detects the attached matter based on an image imaged by the imaging device, wherein the light source emits light that flickers at a drive frequency different from the imaging frequency, and the imaging device receives the reflected light via an optical filter that selects and transmits the reflected light, and the attached matter detection processor detects a beat on an image generated by a difference between the imaging frequency and the drive frequency, and identifies an image region where the beat is detected as an attached matter image region.

1 . An attached matter detector comprising:
 a light source that emits light to a transparent member;   an imaging device that receives light that is emitted from the light source and reflected by attached matter attached on the transparent member by an image sensor, a light-receiving element of which is structured by a two-dimensionally-arranged imaging pixel array, and consecutively images an image of the attached matter attached on the transparent member at a predetermined imaging frequency; and   an attached matter detection processor that detects the attached matter based on an image imaged by the imaging device,   
       wherein the light source emits light that flickers at a drive frequency that is different from the imaging frequency, and the imaging device receives the reflected light by the image sensor via an optical filter that selects and transmits the reflected light, and the attached matter detection processor detects a beat on an image generated by a difference between the imaging frequency and the drive frequency, and identifies an image region where the beat is detected as an attached matter image region where the attached matter is shown. 
     
     
         2 . The attached matter detector according to  claim 1 , wherein one of the drive frequency and the imaging frequency is set to deviate from an integral multiple of the other. 
     
     
         3 . The attached matter detector according to  claim 2 , wherein the light source emits light of a specific wavelength range, and the optical filter includes an optical filter that selects and transmits the specific wavelength range. 
     
     
         4 . The attached matter detector according to  claim 3 , wherein the optical filter includes an optical filter that selects and transmits a specific polarization component. 
     
     
         5 . The attached matter detector according to  claim 4 , wherein the attached matter detection processor compares a plurality of images imaged at different times, and detects the beat. 
     
     
         6 . The attached matter detector according to  claim 5 , wherein the attached matter detection processor detects the beat based on difference information between the plurality of images imaged at different times. 
     
     
         7 . The attached matter detector according to  claim 6 , wherein the imaging device obtains image data in a unit of one image line, or equal to or more than two image lines on the image sensor at a predetermined signal acquisition frequency, and images an image of the attached matter, and the attached matter detection processor detects the beat by comparing a pixel value between the plurality of images per unit image region obtained by dividing an imaged image into a plurality of regions, and a value of the number of an image line converted from a size in an arrangement direction of the image line in the unit image region is set smaller than a value of the number of an image line from a cycle of a beat generated by a difference between the signal acquisition frequency and the drive frequency. 
     
     
         8 . The attached matter detector according to  claim 7 , comprising:
 an imaging frequency changer that performs control that increases an imaging frequency of the imaging device, when changing from a state where the attached matter is not detected by the attached matter detection processor to a state where the attached matter is detected.   
     
     
         9 . The attached matter detector according to  claim 8 , comprising:
 a light emission intensity adjuster that determines whether image data from the image sensor shows a saturation value, when the attached mater is detected by the attached matter detection processor, and adjusts light emission intensity of the light source based on the determination result.   
     
     
         10 . An attached matter detection method, comprising the steps of:
 emitting light to a transparent member from a light source;   receiving reflected light by attached matter attached on the transparent member by an image sensor, a light-receiving element of which is two-dimensionally structured by an imaging array, and consecutively images an image of the attached matter at a predetermined imaging frequency; and   detecting the attached matter based on an imaged image, wherein the light source that emits light that flickers at a drive frequency that is different from the imaging frequency is used, the reflected light is received by the image sensor via an optical filter that selects and transmits the reflected light, a beat on an image generated by a difference between the imaging frequency and the drive frequency is detected, and an image region where the beat is detected is identified as an attached matter image region where the attached matter is shown.